The lithium ion battery separator thickness uniformity of the direct impact on the quality of the appearance of the diaphragm volume so that the intrinsic performance is one of the strict control of production process quality indicators.
Production line in the high degree of automation of the diaphragm, the diaphragm thickness are based on the online high precision non-contact thickness gauges and fast feedback control system for automatic detection and control. The uniformity of thickness of the diaphragm, including the vertical thickness uniformity and lateral thickness uniformity. The lateral thickness uniformity is particularly important. Generally require control within ± 1 micron.
Mechanical properties
The mechanical properties of the diaphragm is an important factor to affect its application, if the diaphragm ruptures, it will short circuit, reducing the yield, thus requiring the process of the battery pack and use the charge and discharge structures, the diaphragm itself has a certain mechanical strength. The mechanical strength of the diaphragm can be used to measure puncture resistance and tensile strength.
Tensile strength and membrane processes associated with the tensile strength of the diaphragm. Uniaxial tension, the film in the stretching direction, strength and vertical direction; while the biaxial stretch, the diaphragm consistency will be similar in both directions. General tensile strength longitudinal strength to reach 100mP transverse strength can not be too over the General Assembly led to the lateral shrinkage increases, this contraction will increase the risk of lithium battery manufacturer, positive and negative contact.
Anti-puncture strength of anti-puncture strength is imposed in a given needle-shaped material used to expose the diaphragm sample quality, and use it to divide trend of short circuit occurs in the assembly process. Due to the diaphragm is sandwiched between rugged positive and negative film, you need a lot of stress. To prevent short circuits, so the diaphragm must have a certain anti-puncture strength. Experience, anti-puncture strength values ??of 300 to 500 g.
Through performance
Through the performance available in a certain period of time and pressure, the amount of membrane gas characterization, mainly reflecting the patency of the lithium ions through the membrane. The size of the diaphragm through the diaphragm porosity, pore size, pore shape and pore twists and turns and so divide the internal pore structure factors affect results.
As a lithium battery separator material itself has a porous structure, porous in the diaphragm material shall be uniformly distributed. Generally in the pore size of 0.03μm ~ 0.12μm, pore size is too small will increase the resistance, too easy to make the positive and negative contacts or dendrites pierce the short-circuit.
Diaphragm manufacturers now basic to the permeability, porosity index to measure the permeability. Porosity is the volume percentage of holes in the volume of the monomer film, and the density of raw materials, resins and films. Existing lithium-ion battery separator porosity between 40% to 50%.
Physical and chemical properties.
Wettability, good wettability and wetting speed is conducive to improve the affinity of the diaphragm and the electrolyte, to expand the contact surface of the diaphragm and the electrolyte, thus increasing the ionic conductivity, improve performance and capacity of battery charge and discharge. Divide on the wettability of the electrolyte through the determination of the liquid absorption rate and liquid holdup measured.
The chemical stability of the membrane in the electrolyte should be maintained long-term stability, no reaction with the electrolyte and electrode material. Its chemical stability is evaluated by measuring the electrolyte corrosion resistance capacity and the expansion and contraction rate.
Thermal stability of the battery charge and discharge process releases heat, especially when a short circuit or overcharge, there will be a lot of heat release. Therefore, when the temperature, the diaphragm should be to maintain the original integrity and mechanical properties of play to isolate positive and negative, to prevent short-circuit the role.
Safety performance as the lithium gradually expanded the scope of application, especially in the field of battery power, the safety of lithium-ion battery to become the most important part of the lithium battery manufacturers. As lithium is the most critical core material, a higher demand on the diaphragm.
Li-ion battery separators generally are able to provide an additional feature is thermal shutdown. This feature can provide an additional security protection for lithium-ion battery. The main parameters of the function of the the obturator temperature and the rupture of membrane temperature.
The obturator temperature microporous closed when the temperature, the exothermic reaction from the heat, charge-off or the battery external short circuit occurs when the internal battery, these cases will have a lot of heat. When the temperature close to the diaphragm melting point, porous closed to form a thermal shutdown, thereby blocking the ions continue to transfer and the formation of the circuit, play a role in the protection of the battery. General PE of 130 ℃ ~ 140 ℃, PP 150 ℃. Rupture of membranes, the temperature refers to the self-heating of the internal battery, external short circuit inside the battery temperature increases, more than closure temperature occlusive micropore blocking current through hot melt performance temperature to rise further, causing the diaphragm rupture, the battery short circuit. Rupture when the temperature is the rupture of membrane temperature. High-quality diaphragm the obturator temperature lower and higher rupture temperature.
China's lithium-ion battery industry development
China is now the global battery manufacturing power, battery production and export volume ranked first in the world. Of lithium-ion battery industry began in late 1997, through an introduction, learning, research and development road of industrialization. The lithium-ion battery production in China in 2000 was only 035 million.
After 2001, with the rapid rise of the lithium-ion battery companies in Shenzhen BYD, BAK, B & K, Tianjin power of God, the lithium-ion battery industry has begun to enter the phase of rapid growth. In 2004 reached 800 million, soared to 38 percent market share in the global market after Japan. In 2005 ~ 2008, China's lithium-ion battery global market share stable at around 34 percent, since the formation of a situation that Japan and South Korea. China's output of lithium batteries is about $ 2 billion in 2010 sales revenue of about 18 billion yuan.
The lithium-ion battery export volume in 2010 was 1.195 billion. Supporting international companies in 2010, Japan accounted for 42%, South Korea accounted for 38%, China accounted for only 18%. The huge demand for lithium-ion battery, lithium battery company in China in the global market share is decreasing competitiveness weakened.
At present, China has developed into a compelling focus for the global lithium industry as one of the world's largest manufacturing base for lithium-ion batteries, BYD, the power of God, BAK, ATL enterprises. The lithium-ion battery manufacturer in Guangzhou, Tianjin, Shandong, Jiangsu, Zhejiang, southern China (Guangdong and Fujian) lithium battery production still accounts for 65% of domestic market share in other provinces accounted for 10%. Lithium production the most representative of the South China region Shenzhen, entrenched BYD, BAK, B & K China Guangdong Bao many famous enterprises, the formation of industrial clusters.
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